Seren's symbol is a necklace bought from any of the elven clan heralds in Prifddinas for 1,000,000 coins. It can be combined with the eight clan symbol pieces, obtained by pickpocketing the respective clan workers or as a rare reward from the Hefin Agility Course, to make a Seren's symbol which gives a total of 270,000 experience in the 18 Prifddinian skills. You cannot combine the symbols with the necklace until you have all eight symbols.